Trump prepared to meet North Korea's Kim

South Korean National Security Director says North Korea will refrain from nuclear tests.

President Donald Trump is prepared to meet North Korean leader Kim Jong Un for the first US-North Korea summit, marking a potentially dramatic breakthrough in nuclear tensions with Pyongyang.

Kim has committed to "denuclearisation" and to suspending nuclear or missile tests, South Korea's National Security Office head Chung Eui-yong told reporters at the White House after briefing Trump.

"A meeting is being planned," Trump tweeted after speaking to Chung, who said that Trump expressed a willingness to sit down with Kim in what would be his biggest foreign policy gamble since taking office.

Chung said Trump, in response to Kim's invitation, had agreed to meet by May, and a senior US official later said it could happen "in a matter of a couple of months, with the exact timing and place still to be determined."

Chung and National Intelligence Service chief Suh Hoon flew to Washington to explain North Korea's stance on possible future talks with Washington and the prospect of Pyongyang suspending nuclear tests if the security of the North's government is assured.

Trump has previously said he was willing to meet Kim under the right circumstances but had indicated that the time was not right for such talks.

"Kim Jong Un talked about denuclearisation with the South Korean Representatives, not just a freeze," Trump said in a message on Twitter on Thursday night.

"Also, no missile testing by North Korea during this period of time."

"Great progress being made but sanctions will remain until an agreement is reached," Trump added.

A meeting between Kim and Trump, who have exchanged bellicose insults in the past year that have raised fear of war, would be a major turnaround after a year in which North Korea has carried out a battery of tests aimed at developing a nuclear-tipped missile capable of hitting the US mainland.

Trump's aides have been wary of North Korea's diplomatic overtures because of its history of reneging on international commitments and the failure of efforts on disarmament by the administrations of President Bill Clinton, President George W. Bush and President Barack Obama.

US officials and experts had earlier cautioned that North Korea could buy time to build up and refine its nuclear arsenal, including a warhead able to survive re-entry into the Earth's atmosphere, if it manages to drag out any talks with Washington.

Japanese Prime Minister Shinzo Abe said he confirmed in telephone talks with Trump that pressure still needed to be applied worldwide on North Korea.

Abe also told reporters he hoped to visit the US as early as next month to meet Trump to discuss North Korea, among other issues.

"We welcome the change in North Korea's stance", Abe said.

A senior US administration official said Trump agreed to meet Kim because Kim is the "one person who is able to make decisions under their authoritarian, uniquely authoritarian, or totalitarian system."